In Magnetic Resonance Imaging (MRI), gradient amplifiers and their associated magnetic field gradient coils are typically used to provide 3-dimensional spatial encoding of atomic spins located in a magnetic field.
These gradient amplifiers are typically characterized by high peak power (several 100 kVA up to 2 MVA for present-day specimens) and high precision of the generated current waveforms. Circuits consisting of series-connected half or full bridges using pulse-width modulation (PWM) have been used to construct gradient amplifiers.
The Japanese patent application JP-08 322815 mentions the problem of improving cooling efficiency of gradient coils and to avoid unnecessary power consumption. This Japanese patent application discloses a magnetic resonance system that is provided with means to cool the gradient coil. It has means to predict the temperature and a means to start cooling when the gradient coil reaches a predetermined temperature.